Differential Diagnosis: Hyponatremia

Marie Chartier, DVM, DACVIM, VCA Roberts Animal Hospital, Hanover, Massachusetts

ArticleLast Updated September 20211 min readPeer Reviewed
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A golden retriever lies on a soft surface, with a catheter inserted into its foreleg, secured with a bandage. The dog appears calm, with its eyes partially closed, indicating a clinical setting for treatment or hydration.

Following are differential diagnoses for patients presented with decreased blood sodium level.

Normal osmolality (290-310 mOsm/kg) 

  • Pseudohyponatremia (eg, hypertriglyceridemia, hyperproteinemia) 

Low osmolality (<290 mOsm/kg)

  • Polyuric renal failure

  • GI fluid loss (eg, vomiting, diarrhea, regurgitation, severe ileus with “pooled” insensible fluid losses) 

  • Hookworm infection

  • Severe dietary sodium restriction

  • Iatrogenic (eg, hypotonic fluids, diuretics)

  • Third-space loss 

    • Pancreatitis

    • Peritonitis

    • Pleural or peritoneal effusion

    • Uroabdomen

  • Hypoadrenocorticism

  • Edematous disorders 

    • Congestive heart failure

    • Liver failure

    • Nephrotic syndrome

  • Syndrome of inappropriate antidiuretic hormone secretion  

  • Psychogenic polydipsia

High osmolality (>310 mOsm/kg)

  • Diabetes mellitus (ie, secondary to hyperglycemia) 

  • Iatrogenic (ie, mannitol administration)